Method and apparatus for determining water content of concrete in the fluid state



Jan. 8, 1952 L GLEGG 2,581,950

' G. METHOD AND APPARATUS FOR DETERMINING WATER CONTENT OF CONCRETE IN THE FLUID STATE Filed July 2'7, 1949 I/vvE/vrme Gale-De l/NDSH/ G4ee Patented Jan. 8, 1952 METHOD AND APPARATUS FOR DETERMIN- ING WATER CONTENT OF CONCRETE IN THE FLUID STATE Gordon. Lindsay Glegg, Kingston Hill, England,

assignor of one-hair to The Square Grip Reinforcement Company (London) Limited, London, England Application July 27, 1949, Serial No. 107,105 In Great Britain July 28, 1948 3 Claims. (01. 175-183) This invention relates to methods of determining the water content of concrete masses when in a fluid condition.

Hitherto, it has been the practice to estimate of the concrete.

crete.

concrete when in a fluid condition.

mass of fluid concrete.

. to the accompanying drawings in which,

partly in section,

shown in Figure 1 and mechanism.

are practically non-conductive.

been eliminated, the homogeneity of the aggregate is destroyed as the heavier constituents thereof gravitate toward the bottom of the mass leaving at the top surface only a thin aqueous This apparatus Inside the container The resist- The resist- The contact 22 is The conthe water content of a concrete mass when in 5 slurry. The electrical resistance of the surface a fluid condition by determining the slump value A mixture will vary with the amount of water This is an indirect method of present for a given mix and accordingly if the estimating the water content of fluid concrete proportions of cement and sand are known it and furthermore slump values give only a rough is possible to ascertain, from a measurement of guide as to the actual water content of the conthe electrical resistance, the water-cement ratio, which is the chief factor in deciding the It is an object of the present invention to strength of the concrete after setting. It is imevolve a method of rapidly and accurately deterportant that the vibration of the mix should mining the water content of any given mass of be continued for a period sufficient to ensure segregation, since the presence of larger aggre- According to the present invention. there is gates in that portion of the mix under test provided a method determining the water conwould introduce unknown factors-which would tent of a mass of fluid concrete which consists render the accurate calculation of the waterin vibrating the fluid concrete until the constitucement ratio impossible. ents thereof segregate, the heavier constituents In Figure 1 there is shown an apparatus for falling to the bottom of the mass whilst the carrying out the determination of the water conlighter constituents remain at and rise to the tent of a mass of fluid concrete. upper zone of the mass and which method furcomprises a container I having two electrodes 2 ther consists in inserting two spaced electrodes and 3 secured to the underside thereof, and proin the mass in the zone in which the lighter vided with a handle 4. constituents tend to segregate, a known E.- M. F. there is located an electric motor 5 which drives being applied across the electrodes and measa shaft 6 having an eccentrically mounted weight urements being made of the maximum current I mounted thereon. The handle 4 is provided passing between the c odes during the vibratwith a press button switch 8. A flexible cable 9 ing operation, the maximum current value being connects the handle 4 to a case [0, which conused as an indication of the water content of the tains (see Fig. 2) a battery ll, an ammeter i5 and resistances I2, 13 and 14. The case also con- For a better understanding of the nature of tains a two-way switch It and a control knob the invention and to show how the same may HA for adjusting the voltage. be carried into effect reference will now be made The elements of the apparatus described above are connected as shown in Figure 2. Figure 1 is a diagrammatic layout of apparatus ances I2 and 13 are connected directly across the for carrying out the method of the invention, battery ll through the switch 8,

ance l3 has a sliding contact I! which can be u e 2 s a cu diagram of the apparatus 40 moved by means of the knob HA. The sliding contact is connected to one terminal 18 of the Figure 3 shows an alternative form of vibrator a t is, th th t in l l9 of whi h i connected to the contact 20 or" the two-way The invention relies upon the observation that switch Hi. The contact 20 can co-operate with whereas a mixture of cement and water has a either the contact 2| or 22. relatively high electrical conductivity, the other connected through a high resistance hi to the constituents of a concrete mix (sand and ballast) negative terminal of the battery ll.

When concrete tact 2| is connected to the electrode 2 and the is consolidated by vibration using for example, electrode 3 is connected directly to the negative a vibrating appliance such as that described and terminal of the battery. The electric motor 5 is illustrated in U. S. Patent.ll To. 2,490,122 the pockets of occluded air which occur during the shovelling or pouring of a wet aggregate are gradually eliminated. If the vibration is conconnected through the switch 8 across the terminals of the battery I l.

Instead of using the motor 5 driving an eccentric weight 1, it is possible to use a vibrating tinued after all the pockets of occluded air have mechanism as cat d in Figure This Vitery I I and the other end ofthecoil is connected to the contact 21. One end of coil 30 ,iscon nected to the positive terminal of the battery and the other end of the coil is connected to'the contact 26. The contact 28 is connected to the negative terminal of the battery II through the switch 8. Condensers are connected across the tion is allowed to continue for a further few moments to see if any increase in the value indicated by the ammeter is obtainable.

f The water content of the: concrete is deduced from the maximum value of current" flowing through the electrodes 2 and 3 as indicated by the ammeter I5, by comparing the value with tables or graphs showing the relationship betwe n water-content and the maximum current. Tables digraphs-are prepared from data obtained as a result of experimental tests, in which the actual watercont'ent of concrete was known, the

water being.weighed before being mixed with the other constituents of the concrete.

In the instrument described above direct cur- I rentoniynasteen used, but it will, of course, be

contacts 26 and 28, and 21 and 28. r

In operation this vibrating mechanism func tions .as follows. When: the contact26 encounters the contact 28 the coil 30 is energised and the end.29 of thearmature is attracted towards the coil 30. Movementof the end 29 towards the coil 38 moves the contact 26 away from thereon tact 28 and eventually thercontact 21 encounters the contact 28.. When this occurs the coil 3| is energised and the end 29 is moved towards coil 3i, thereby breaking the circuit of the coil 3I by the. movement of .the contact Z'Laway from the contact 28. Continued movement-pf the armature 23 in thismanner produces vibration sufficient to vcause segregation of the concrete into which thercontainer, I may be inserted.

Use of the apparatus shown in Eigures 1 and 2 is effected as, follows. The switch 8 is closed 1'!- ,ensurethat the E. M. F. applied across the electrodes 2 and- 3 is always the same for each individual test, the control l nob I IA is m ilipulated until the ammeter indicates a standard current. The position of the two-way switch is then altered so, that contact I 29 encounters contact 2|. The container I is then pushed into the concrete mass which it is desired to test, the

electrodes 2 and 3 beingcornpletely submerged in the concrete. The vibration of the container caused by the motor 5 having the eccentric weight I promotes local segregation of the concrete in the vicinity of the container, and as the stones and heavy aggregatesink, a mixture of watencement and sand risesto the top. As the mixture of water sand andv cement rises to the top the current-fiowing 'through the electrodes indicated by the ammeterincreases. The container I is gradually withdrawn from the concrete until theelectrodes 2 a'ndfi just touch the surface of the concrete, andthen the current indicatedby the ammeter is read. Actually the operator merely has to read the maximumlvalue indicated by the'ammeter, whilst the container is being withdrawn from the concrete, and if the operator is in any doubt as to whetherthe concrete has been su'mcientiy segregated. the vibraappreciated that alternating current could be used instead.

I claim:

1. A method otdetermining the water content of a mass ot fluid concrete which consists in vibrating the fluid concrete until the constituents thereofsegregate, the heavier constituents falling to the bottom of the mass whilst the lighter constituents remain at and rise to the upper zone of the mass, and which method further consists in inserting two spaced. electrodes in the I mass in the zone in which the lighter constituents tend to segregate, a known E. M. F. being ap plied across the electrodes and measurements be ing' made of the maximum current passing between the electrodes 'during the vibrating operation, the maximum current value being used as an indication of the water content of the mass of fluid concrete.

2. A method as claimed in claim 1, wherein the determination of the maximum current is made upon the withdrawal of the electrodes from the mass, the withdrawal being made in such direction that the electrodes pass through the zone of the mass containing the least solid constituents.

3. Apparatus for determining the water content of fluid concrete comprising supporting means, a pair of electrodes for insertion in the fluid concrete; said electrodes being located in spaced relation upon the supporting means, a vibrator for vibrating the concrete under test to cause local segregation of the concrete mix in the vicinity of the vibrator, said vibrator being mounted on the supporting means, means for suppl ing electrical current to the electrodes and means'fo'r the measurement of said current.

GORDON LINDSAY REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name Date 1,279,143 Patterson Sept. 17, 1918 1,756,286 Farrall et al a. Apr. 29, 1930 1,930,831 Webb .2 Oct. 17, 1933 2,466,453 Locke Apr. 5, 1949 2,468,972 Hagerty May 3, 1949 

